Hi Steffo!
I referee for a derby team in my town. Do you know if your team is part of WFTDA, a national roller derby league? They have rules about TG skaters, that you must have hormone levels in the biological female range and be living full time as a woman. No surgery required though, which is nice.
Even if you can't skate with them now, don't be shy about getting involved as a ref or NSO. That way, if/when you begin hormones, you'll have a leg up. Plus, it's soooo much fun!
Cheers!